Within the temperature range 288-343 K and frequencies 10-1-10 6 Hz, the dielectric properties of planar and homeotropic oriented nematic liquid crystal 6CHBT with the impurity of 0-3 wt.% Ni-TMTAA-TCNQ molecules have been investigated. It has been shown that at the lowest frequencies, the dispersion of components of the complex dielectric permittivity in the case of a planar oriented liquid crystal is caused by oscillations of molecular dipoles within the range of angles corresponding to fluctuations of the order parameter under the action of electric field. The values of relaxation times have been estimated, and it has been shown that with the increase in the impurity concentration, the value of the relaxation time decreases. The temperature dependences of the values inverse to the relaxation time have been analyzed. It has been shown that for the middle frequency range the obtained dielectric spectra characterize the bulk properties of the samples, in particular the value of the electrical conductivity. It has been found that with increasing the molecular concentration, the activation energy for the temperature dependence of the electrical conductivity increases. This dependence for the whole range of studied temperatures correlates with the temperature dependence of the values inverse to the relaxation time. It has been shown that at the concentration of the impurity up to 1 wt.%, the conductivity of the samples both in homeotropic and planar orientations of molecules varies according to the power law of the impurity concentration. It has been estimated the value of the exponent for the concentration dependence of conductivity, and it has been shown that it is the same for various molecular orientations.
The dielectric properties of planar-oriented nematic liquid crystal E25M with Li-TCNQ impurities have been investigated within the frequency range 10-1 …10 6 Hz and temperatures 298…343 K. The concentration of impurities varied between 0 and 0.1 wt.%. It has been shown that the presence of a small impurity of Li-TCNQ in liquid crystal increases electrical conductivity, influences on the value of the conductivity activation energy in the nematic phase and practically does not change the activation energy in the isotropic phase. The times of dielectric relaxation τ for the low-frequency part of the spectrum of complex dielectric constant components have been estimated. It has been shown that, within the frame of existence of the liquid crystal phase, the temperature dependence of τ-1 linearly depends on the inverse value of the temperature in the Arrhenius coordinates and is well agreed with the temperature dependence of conductivity.
Abstract. Solutions of fullerene molecules С60 with chemically attached molecules of diamine (С60D) in planar oriented nematic liquid crystal (NLC) were obtained by only heating and ultrasonic processing. The С60D concentration changes from 0 up to 3.0 wt.%. Within the ranges of frequencies 10 -1 -10 6 Hz and temperatures 298-343 K, dielectric properties of solutions were investigated. It was shown that, at frequencies higher than 100 Hz, the frequency dispersion of the components of complex dielectric permittivity is absent. A value of conductivity of the solution was determined. It was also shown that the activation energy for the temperature dependence of the conductivity in nematic and isotropic phases does not depend on the concentration of molecules С60D. Obtained and explained were the reasons of the nonmonotonic conductivity dependence of solutions on the concentration of С60D molecules. For frequencies lower than 100 Hz, the dispersion of the components of complex dielectric permittivity is observed. It was shown that the dispersion can be described by the Debye equation. The temperature dependence of a value inverse to the relaxation time correlates with the temperature dependence of conductivity. Presence of С60D molecules in NLC tends to increasing the voltage for the Frederiksz transition. Made was the assumption that this effect may be explained by increase in viscosity of NLC as a consequence of aggregation of fullerene molecules.
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